Various types of rigid boards are currently manufactured for use in industry. These include chip board, oriented strand board ("OSB"), medium density fibre board ("MDF)" and particle board. Generally, each of these boards comprises a mixture of wood (e.g. wood chips, saw dust, fibrous wood) and a formaldehyde based binder. Formaldehyde binders are thermosetting compounds and accordingly, the boards are formed under elevated temperatures and pressure.
There are several disadvantages with current board products. Boards which are constructed with formaldehyde binders typically release small amounts of formaldehyde into the atmosphere over an extended period of time (e.g. 10 years). OSB and particle board which are used in the construction of housing, as well as MDF which is used in the construction of furniture, therefore typically release formaldehyde into the air in a house, office or other dwelling. Formaldehyde vapours tend to cause a portion of the population discomfort (e.g. headaches). Recent health concerns have been raised by the emission of formaldehyde from such products.
A further disadvantage with wood based board products is the requirement of wood, either wood chips, saw dust, fibre wood and the like, as a feed material. The improvement in sawing and planing machinery has reduced the amount of wood bi-products produced by lumber mills. At the same time, other uses for wood bi-products, such as for use as fuel, has increased.
In recent years, different processes have been used in an attempt to reduce the reliance upon formaldehyde binders and wood chips. For example, U. S. Pat. No. 4,882,112 discloses a process for producing sheets or other shaped articles which includes applying a solution or dispersion of a hydrophilic urethane prepolymer in a large excess of water, optionally containing an inert binder polymer, to vegetable particulate materials, shaping the resulting mass, curing the shaped article at room temperature or an elevated temperature (e.g. about 22.degree. C.) and drying the shaped article. One disadvantage of this process is the large amount of time which is required in curing and drying the shaped article. Example 2 exemplifies the production of a flexible sheet of about 8 mm thickness. The sheet required three minutes to cure and three hours to dry subsequent to the curing.